Metal laminate

Abstract

To provide a metal-clad laminate satisfying all of dielectric properties, heat resistance and dimensional stability with a high level and having high bending resistance.SOLUTION: A metal-clad laminate is provided which includes a first fluororesin layer, polyimide layers, a second fluororesin layer and metal foil. The first fluororesin layer contains polytetrafluoroethylene and a powdered filler. The polyimide layers are provided on both sides of the first fluororesin layer, respectively and include polyimide. The second fluororesin layer is provided on the polyimide layer and includes perfluoro-alkoxy alkane. The metal foil is provided on the second fluororesin layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a metal-clad laminate. [Background technology]

[0002] As the information and communications environment has become more diverse and sophisticated in recent years, communication systems using high-frequency bands have been attracting attention. Among high-frequency bands, the so-called millimeter waves, which are high frequencies above 30 GHz, have a very large information transmission capacity, but are characterized by their tendency to have large transmission losses. Therefore, there is a growing demand for low-loss millimeter-wave substrates that can reduce transmission losses even when transmitting millimeter waves.

[0003] Because fluororesin is a material with excellent dielectric properties, laminates that include a dielectric material containing fluororesin and a metal foil as a conductor are used in a variety of high-frequency applications. In such laminates, electrical signals pass through the interface between the dielectric and the conductor, and the smoother the interface, the smaller the transmission loss.

[0004] On the other hand, fluororesins have a large thermal expansion coefficient and therefore lack dimensional stability. Therefore, flexible cupper clad laminates (FCCLs), which have a polyimide layer with a low thermal expansion coefficient, are used as laminates for high-frequency bands. However, polyimides do not necessarily have excellent dielectric properties, so metal-clad laminates that satisfy all of the requirements for high levels of dielectric properties, heat resistance, and dimensional stability have not yet been obtained. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-011456 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-024265 Summary of the Invention [Problem to be solved by the invention]

[0006] In addition to these properties, FCCL is also required to have, for example, high bending resistance. As flexible printed circuits (FPCs) become thinner, the amount of deflection due to their own weight increases, making them difficult to handle during processing. This can be suppressed if FCCL has high bending resistance. Polyimide has the property of having a higher bending resistance than polytetrafluoroethylene (PTFE).

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a metal-clad laminate which satisfies all of the requirements for dielectric properties, heat resistance and dimensional stability at high levels, and also has high bending resistance. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided a metal-clad laminate having a total thickness in the range of 50 μm to 200 μm. , th The laminate comprises a first fluororesin layer, a polyimide layer, a second fluororesin layer, and a metal foil. The first fluororesin layer contains polytetrafluoroethylene and a powdered filler. The polyimide layers are provided on both sides of the first fluororesin layer and contain polyimide. The second fluororesin layer is provided on at least one of the polyimide layers and contains a perfluoroalkoxyalkane. The metal foil is provided on the second fluororesin layer. The PI thickness ratio, expressed as ([total thickness of polyimide layers] / [total thickness of dielectrics]) x 100, is within the range of 10 to 25%. The total thickness of the dielectric is the thickness of the metal-clad laminate excluding the metal foil. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a metal-clad laminate that satisfies all of the requirements for dielectric properties, heat resistance, and dimensional stability at high levels, and also has high bending resistance. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view schematically showing an example of a metal-clad laminate according to an embodiment. [Figure 2] FIG. 10 is a cross-sectional view schematically showing another example of a metal-clad laminate according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes the embodiments with reference to the drawings as appropriate. Note that common components throughout the embodiments are designated by the same reference numerals, and redundant explanations will be omitted. The drawings are schematic diagrams for explaining and facilitating understanding of the embodiments, and the shapes, dimensions, ratios, etc. may differ from those of actual devices. However, these can be appropriately modified in design, taking into consideration the following explanation and known techniques.

[0012] A metal-clad laminate according to an embodiment will be described with reference to the drawings.

[0013] 1 is a cross-sectional view schematically illustrating an example of a metal-clad laminate. The metal-clad laminate 10 may be a printed circuit board having a pattern circuit formed by etching a metal foil. The metal-clad laminate may be mounted in various devices such as image sensors, collision prevention vehicle radar, and high-capacity wireless communication systems primarily based on applications such as IoT (Internet of Things) and 5G.

[0014] The metal-clad laminate 10 comprises a first fluororesin layer 1, a polyimide layer 2, a second fluororesin layer 3, and a metal foil 4. The laminate consisting of the first fluororesin layer 1, the polyimide layer 2, and the second fluororesin layer 3, excluding the metal foil 4, can constitute a dielectric 5. A polyimide layer 2 is provided on each side of the first fluororesin layer 1. By providing two polyimide layers 2 on both sides of the first fluororesin layer 1, deformation (flaring and wrinkling) of the polyimide layer 2 can be suppressed. If a polyimide layer were provided on only one side of the first fluororesin layer, the polyimide layer would tend to deform due to differences in the linear expansion coefficient and contraction force between the first fluororesin layer and the polyimide layer. In the metal-clad laminate according to the embodiment, the polyimide layers 2 are provided on both sides of the first fluororesin layer 1, thereby improving the mechanical strength and dimensional stability of the first fluororesin layer 1 or the entire metal-clad laminate 10.

[0015] Metal-clad laminates with suppressed deformation of the polyimide layer are free from curl and warpage and have a high level of smoothness. Lead-free mounting is becoming more common due to the need to increase the density of printed wiring boards and reduce environmental impact. As a result, suppressing board warpage during mounting is becoming increasingly important. If a warp-resistant FCCL can be provided, poor connections between components and boards due to board warpage during mounting can be suppressed, ensuring high connection reliability.

[0016] The first fluororesin layer contains polytetrafluoroethylene (PTFE) and a powdered filler. The first fluororesin layer has a sheet or film shape. PTFE has excellent dielectric properties, so a metal-clad laminate including the first fluororesin layer can be used in high frequency bands. The first fluororesin layer may be made of PTFE and a powdered filler. PTFE has a high melting point and a high maximum continuous use temperature, so the first fluororesin layer can improve the heat resistance of the metal-clad laminate.

[0017] For example, lead-free solder, which has a higher melting point than lead-containing solder, can be used to process a substrate in which the first fluororesin layer contains PTFE. A metal-clad laminate including a first fluororesin layer containing PTFE can have a continuous heat resistance of 260°C or higher. The heat resistance of the metal-clad laminate can be evaluated by a solder heat resistance test in accordance with JIS C 6481.

[0018] The powdered filler can be an inorganic filler and / or an organic filler. When the first fluororesin layer contains a powdered filler, the coefficient of thermal expansion (CTE) of the first fluororesin layer can be reduced compared to when the first fluororesin layer does not contain a powdered filler. The volume ratio of the powdered filler in the first fluororesin layer is, for example, in the range of 10% to 70%, and preferably in the range of 40% to 60%. If this ratio is too small, the coefficient of thermal expansion of the dielectric including the first fluororesin layer may be too large. If this ratio is too large, the mechanical strength (bending resistance) of the dielectric tends to be insufficient.

[0019] Examples of inorganic fillers include silica (silicon dioxide), clay, talc, calcium carbonate, mica, diatomaceous earth, alumina, zinc oxide, titanium oxide, calcium oxide, magnesium oxide, iron oxide, tin oxide, antimony oxide, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, basic magnesium carbonate, magnesium carbonate, zinc carbonate, barium carbonate, dawsonite, hydrotalcite, calcium sulfate, barium sulfate, calcium silicate, montmorillonite, bentonite, activated clay, sepiolite, imogolite, sericite, glass fiber, glass beads, silica-based balloons, carbon black, graphite, carbon fiber, carbon balloons, wood flour, and zinc borate. The first fluororesin layer may contain one type of inorganic filler or two or more types of inorganic fillers. The particle surfaces of the inorganic filler may be subjected to a hydrophobic treatment.

[0020] Examples of the organic filler include polyimide powder and LCP (liquid crystal polymer) powder.

[0021] To enhance the effect of reducing the coefficient of thermal expansion, the powder filler is preferably an inorganic filler. Among inorganic fillers, spherical fine particles made of silicon dioxide with a hydrophobic surface are preferred. In this case, the silicon dioxide provides a low CTE, the hydrophobic surface treatment reduces moisture absorption, the spherical fine particles maintain flexibility, and the overall dielectric loss tangent Df is suppressed.

[0022] The average particle size of the powdered filler is, for example, in the range of 0.5 μm to 30 μm. The average particle size of the powdered filler can be measured by removing the metal foil and polyimide layer from the metal-clad laminate, and then removing the fluororesin by thermal decomposition, and observing the resulting residue with a scanning electron microscope (SEM).

[0023] The thickness of the first fluororesin layer is, for example, in the range of 10 μm to 75 μm, and preferably in the range of 25 μm to 75 μm. A thickness of the first fluororesin layer in the range of 25 μm to 75 μm is preferable from the viewpoint of dielectric properties. Furthermore, in this case, there is an effect of improving the handleability of the film corresponding to the first fluororesin layer during production.

[0024] The polyimide layer contains polyimide. The polyimide layer has a sheet or film shape. The polyimide layer may consist solely of polyimide. The polyimide contained in the polyimide layer may be a high heat-resistant polyimide or a thermoplastic polyimide. The polyimide contained in the polyimide layer may consist solely of a high heat-resistant polyimide. In this case, the bending resistance of the metal-clad laminate can be further increased. Modified polyimide (MPI) may be used as the polyimide. The polyimide layer may further contain a fluororesin such as PTFE and PFA, and a different material such as a powdered filler.

[0025] The compositions of the two polyimide layers provided on both sides of the first fluororesin layer may be the same as or different from each other.

[0026] Thermoplastic polyimide refers to polyimide having a softening point of less than 300°C. The softening point is the temperature at which an object suddenly softens. For amorphous polyimides, the softening point is the glass transition point Tg. For crystalline polyimides, the softening point is the melting point. The softening point of thermoplastic polyimides is preferably within the range of 200°C to 300°C.

[0027] An example of a thermoplastic polyimide is AURUM (registered trademark) manufactured by Mitsui Chemicals, Inc. AURUM (registered trademark) has a glass transition temperature Tg of 250°C and a melting point Tm of 388°C.

[0028] The highly heat-resistant polyimide refers to a polyimide having a glass transition temperature Tg of 320°C or higher or a Tg higher than the thermal decomposition temperature. The molecular structure of the highly heat-resistant polyimide is not particularly limited as long as it contains 90% by mass or more of a non-thermoplastic polyimide.

[0029] The high heat-resistant polyimide can be produced, for example, using polyamic acid as a precursor. When the polyimide layer contains a high heat-resistant polyimide, the glass transition temperature Tg of the high heat-resistant polyimide is preferably higher than the melting temperature Tm of the fluororesin contained in the second fluororesin layer in contact with the polyimide layer. The glass transition temperature Tg of the high heat-resistant polyimide is more preferably 10°C or more higher than the melting temperature Tm of the fluororesin contained in the second fluororesin layer.

[0030] When processing the adhesion between the polyimide layer and the second fluororesin layer, it is desirable to process at a temperature equal to or higher than the melting point (Tm) of the fluororesin contained in the second fluororesin layer + 10°C. If the glass transition point (Tg) of the high heat-resistant polyimide is equal to or higher than this processing temperature, the adhesion between the polyimide layer and the second fluororesin layer can be improved.

[0031] For example, when the melting point Tm of the fluororesin contained in the second fluororesin layer is in the range of 290° C. to 310° C., the glass transition point Tg of the high heat resistant polyimide is preferably 320° C. or higher. Examples of high heat resistant polyimides having a glass transition point Tg of 320° C. or higher include Kapton (registered trademark) manufactured by DuPont Corporation, UPILEX-S (registered trademark) manufactured by Ube Industries, Ltd., and XENOMAX (registered trademark) manufactured by Xenomax Japan Co., Ltd.

[0032] Examples of modified polyimides include those obtained by mixing a small amount of a monomer other than polyimide when polymerizing a monomer such as polyamic acid to reduce the purity, those obtained by bonding a low-molecular-weight oligomer other than polyimide, and those obtained by polymerizing a monomer into which another substituent has been introduced together with the monomer.

[0033] Each polyimide layer is preferably thinner than the first fluororesin layer. Furthermore, it is more preferable that the total thickness of the polyimide layers included in the metal-clad laminate is thinner than the first fluororesin layer. Polyimide has a higher moisture absorption rate than fluororesin. Therefore, by reducing the thickness ratio of the polyimide layers and increasing the thickness ratio of the first fluororesin layers, the dielectric properties are improved.

[0034] The total thickness of the polyimide layers (total thickness of the two layers) relative to the total thickness of the dielectric excluding the metal foil 4 in the metal-clad laminate is defined as the "PI thickness ratio." That is, the PI thickness ratio is expressed by the following formula (1). The PI thickness ratio in the metal-clad laminate is, for example, in the range of 10 to 25%. When it is in this range, it is possible to achieve both the advantages of fluororesin, namely low dielectric properties and low moisture absorption, and the advantages of polyimide, namely high mechanical strength. Therefore, in this case, it is preferable because it is easy to ensure an appropriate balance of properties as a dielectric for FCCL. [ PI thickness ratio] = ( [Total thickness of polyimide layer] / [Total thickness of dielectric] × 100…(1)

[0035] The thickness of each polyimide layer is, for example, in the range of 5 μm to 15.0 μm. The total thickness of the polyimide layers included in the metal-clad laminate can be adjusted appropriately depending on the total thickness of the dielectric, but is, for example, in the range of 10 μm to 50 μm, and preferably in the range of 10 μm to 30 μm.

[0036] In the dielectric 5, the two polyimide layers 2 are provided so as to face the front and back surfaces of the first fluororesin layer 1, respectively. For example, as shown in FIG. 1, in the dielectric 5 configured in plane symmetry, the first fluororesin layer 1 is disposed in a position close to an imaginary plane of symmetry (not shown), while the two polyimide layers 2 are disposed in positions away from the plane of symmetry. In this way, since the polyimide layer 2, which has a relatively higher hardness than the first fluororesin layer 1, is disposed on the outer side of the dielectric 5, the metal-clad laminate 10 exhibits high bending resistance. This is also true in the case of FIG. 2, in which the dielectric 5 does not have a completely plane-symmetric structure. The dielectric according to the embodiment does not need to have a plane-symmetric laminate structure.

[0037] A second fluororesin layer 3 is provided on the polyimide layer 2. As shown in Fig. 1, the second fluororesin layer 3 may be provided on each surface of two polyimide layers 2 provided on both sides of the first fluororesin layer 1, or as shown in Fig. 2, the second fluororesin layer 3 may be provided on only one of the two polyimide layers 2. A metal foil 4 is provided on the second fluororesin layer 3. Although not shown, a second fluororesin layer 3 may further exist between the first fluororesin layer 1 and the polyimide layer 2.

[0038] The second fluororesin layer 3 contains perfluoroalkoxyalkane (PFA). Because PFA is a fluororesin with melt flowability, the second fluororesin layer 3 can function as a layer that bonds the polyimide layer 2 and the metal foil 4. The presence of the second fluororesin layer 3 between the polyimide layer 2 and the metal foil 4 can improve the peel strength of the metal foil 4. The second fluororesin layer 3 is preferably made only of PFA. This is because if the second fluororesin layer 3 contains other components such as an inorganic filler, the brittleness of the second fluororesin layer 3 may increase, resulting in a decrease in peel strength.

[0039] The thickness of the second fluororesin layer 3 is, for example, in the range of 1 μm to 20 μm, and preferably in the range of 2 μm to 12 μm. If the thickness of the second fluororesin layer 3 is less than 1 μm, it may be difficult to obtain the effect of improving the peel strength attributable to the second fluororesin layer 3. For example, there is a risk that the peel strength at the interface between the second fluororesin layer and the metal foil or polyimide layer may be extremely reduced. If the thickness of the second fluororesin layer 3 is too great, the material before metal-clad lamination processing tends to curl significantly, resulting in poor handleability.

[0040] The thickness of the dielectric is, for example, in the range of 25 μm to 100 μm, and preferably in the range of 50 μm to 100 μm. When the thickness of the dielectric is in this range, continuous molding of the FCCL becomes easy and sufficient flexibility can be exhibited.

[0041] The peel strength of the metal foil 4 at room temperature is preferably 1.0 kN / m or more, and more preferably 1.2 kN / m or more. In order to increase the peel strength of the metal foil 4, it is effective to use an adhesive modified PFA as the PFA contained in the second fluororesin layer. When the second fluororesin layer contains an adhesive modified PFA, it becomes easy to achieve a peel strength of 1.0 kN / m or more of the metal foil 4. The second fluororesin layer may be composed only of adhesive modified PFA. The peel strength of the metal foil can be measured by a 90° peel test in accordance with JIS C 6481 at room temperature.

[0042] The adhesive modified PFA further comprises a modified monomer unit that provides improved adhesion to, for example, metal foil.

[0043] Adhesive modified PFA is melt-moldable and has the same heat resistance, chemical resistance, weather resistance, low friction, non-stickiness, water and oil repellency, and dielectric properties as regular PFA. The dielectric constant of the adhesive modified PFA at a frequency of 1 GHz is preferably 2.06 or less, and the dielectric dissipation factor is preferably 0.002 or less. The dielectric constant and dielectric dissipation factor of the adhesive modified PFA resin can be measured in accordance with JIS 2138:2007. When the dielectric constant and dielectric dissipation factor of the adhesive modified PFA resin satisfy the above numerical ranges, the metal-clad laminate can have excellent low-loss characteristics.

[0044] The adhesive modified PFA preferably has a melt flow rate in the range of 10 g / 10 min to 25 g / 10 min. The adhesive modified PFA has a tensile strength of, for example, 35 MPa or more. The adhesive modified PFA has a flexural modulus of, for example, 600 to 680 MPa. The adhesive modified PFA has a melting point of, for example, 290°C to 300°C.

[0045] An example of an adhesive modified PFA is Fluon+ EA-2000 manufactured by AGC Corporation.

[0046] The type of metal foil is not particularly limited and may be appropriately selected depending on the application of the metal-clad laminate. For example, when the laminate is used in an electronic device, examples of the material for the metal foil include copper or copper alloy, stainless steel or its alloy, nickel or nickel alloy, and aluminum or aluminum alloy. Copper foils such as rolled copper foil and electrolytic copper foil are commonly used in ordinary laminates used in electronic devices, and copper foil is also suitable for the laminate according to the embodiment. A rust-preventing layer (oxide film such as chromate) or a heat-resistant layer may be formed on the surface of the metal foil.

[0047] The surface roughness Rz of the metal foil 4 on the surface where the metal foil 4 and the second fluororesin layer 3 come into contact is, for example, 3.0 μm or less, and preferably 1.0 μm or less. As long as the peel strength of the metal foil is 3 N / cm or more, it is desirable that the surface roughness Rz be as small as possible. For example, the surface roughness Rz may be 0.5 μm or more. In this specification, the surface roughness Rz refers to the "maximum height Rz" measured in accordance with JIS C 6515-1998.

[0048] The thickness of the metal foil is not particularly limited as long as it can exhibit sufficient functionality depending on the application of the metal-clad laminate. The thickness of the metal foil is, for example, in the range of 2 μm to 18 μm, and preferably in the range of 9 μm to 18 μm.

[0049] The total thickness of the metal-clad laminate is, for example, in the range of 50 μm to 200 μm, and preferably in the range of 70 μm to 136 μm.

[0050] The dielectric constant (Dk) of the dielectric portion excluding the metal foil is preferably 3.5 or less, more preferably 3.0 or less, and the dielectric loss tangent (Df) of the dielectric portion is preferably 0.0030 or less, more preferably 0.0020 or less.

[0051] The metal-clad laminate according to the embodiment achieves the high dimensional stability and mechanical strength inherent in polyimide, while allowing the thicknesses of the first and second fluororesin layers to account for a large proportion of the metal-clad laminate's thickness. Furthermore, the first fluororesin layer containing PTFE is sandwiched between two polyimide layers. Therefore, the metal-clad laminate according to the embodiment satisfies all of the requirements for dielectric properties, heat resistance, and dimensional stability at high levels, and also has a high bending resistance.

[0052] To obtain the metal-clad laminate according to the embodiment, for example, the layers are laminated in the order shown in Fig. 1 or 2, and then the laminate is hot-pressed under predetermined pressure and temperature conditions and cooled. In this way, a single product in which the layers are integrated is obtained. The second fluororesin layer may be produced by applying an aqueous or organic solvent-based dispersion liquid in which PFA resin particles are dispersed to the desired film and drying it.

[0053] The hot pressing method is not particularly limited, and known methods such as an upper and lower flat plate method, a two-roller method, and a belt press method can be used. To prevent thermal discoloration of the metal foil, it is desirable to perform the hot pressing under vacuum, nitrogen gas, or other inert atmosphere. Furthermore, using a thick polyimide film as a protective film during hot pressing can further prevent thermal discoloration and is also expected to reduce wrinkles in each layer (function as a buffer material).

[0054] The hot pressing can be carried out for, for example, 60 to 150 minutes. The temperature during pressing can be set, for example, within a range of room temperature to 400°C, and preferably within a range of 330°C to 360°C.

[0055] The pressing pressure is, for example, 5 kg / cm 2 ~50kg / cm 2 It is possible to set the pressure within the range of 0.01 to 0.01 mm. It is also possible to set the pressure without applying any pressure. If the pressure is insufficient, the peel strength of the metal foil tends to be poor. If the pressure is too high, the dimensions of the laminate may change, which is undesirable.

[0056] The degree of vacuum can be set, for example, within the range of 0.1 Torr to 800.0 Torr. If the degree of vacuum is too low, air may be trapped between the layers of the materials, which may cause delamination and / or oxidation of the metal foil. If the degree of vacuum is too high, the materials may slip and collapse.

[0057] [Example] Examples will be described below, but the embodiments are not limited to the examples described below.

[0058] Example 1 Materials (sheets) for constituting each layer were prepared as shown below.

[0059] A first film constituting a first fluororesin layer was prepared. The first film was a film containing PTFE and silicon dioxide. The content of silicon dioxide contained in the first film was 48 wt %, and its average particle diameter was 2 μm. The thickness of each first film was 43 μm. Two sheets of this first film were prepared.

[0060] As the second film constituting the second fluororesin layer, EA-2000 manufactured by AGC Inc. was prepared. EA-2000 is a fluororesin film made essentially of adhesive modified PFA resin. Four second films each having a thickness of 3 μm and two second films each having a thickness of 2 μm were prepared.

[0061] Two sheets of UPILEX-12.5SN polyimide films were prepared as polyimide layers. These polyimide films were made of non-thermoplastic polyimide. Each polyimide film had a thickness of 12.5 μm.

[0062] Two sheets of electrolytic copper foil manufactured by Fukuda Metal Foil & Powder Co., Ltd. were prepared as the metal foils constituting the metal foil layer. The surface roughness Rz of one side (matte side) of the electrolytic copper foil was 0.8 μm. The thickness of each electrolytic copper foil was 15 μm.

[0063] The films and metal foils prepared as described above were laminated in the lamination order (arrangement order) shown in Table 1 below. When laminating the films, they were laminated so that their MD directions were aligned with each other. In this way, a laminate before pressing was produced. In addition to the lamination order of the films and metal foils, Table 1 below also shows the thickness of the laminate before pressing and the thickness of the metal-clad laminate after pressing.

[0064] [Table 1]

[0065] The obtained laminate was carried into a clean room and then subjected to hot pressing for 60 minutes to produce a metal-clad laminate. As shown in Table 1, the total thickness of the obtained metal-clad laminate was 154 μm. The thickness of the dielectric contained in the metal-clad laminate was 124 μm. The PI thickness ratio in the metal-clad laminate according to Example 1 was 20%.

[0066] (Comparative Example 1) A metal-clad laminate according to Comparative Example 1 was produced under the same conditions as in Example 1, except that the order in which the films and metal foils were stacked was changed as shown in Table 2 below when producing the laminate. In Table 2 below, in addition to the order in which the films and metal foils were stacked, the thickness of the laminate before pressing and the thickness of the metal-clad laminate after pressing are also shown.

[0067] [Table 2]

[0068] As shown in Table 2, the total thickness of the obtained metal-clad laminate was 153 μm. The thickness of the dielectric contained in the metal-clad laminate was 123 μm. The PI thickness ratio in the metal-clad laminate according to Comparative Example 1 was 20%.

[0069] The metal-clad laminates produced in Example 1 and Comparative Example 1 were subjected to various measurements as described below.

[0070] <Measurement of linear thermal expansion coefficient> The coefficient of linear thermal expansion (CTE) was measured in the longitudinal (X) direction (MD) and transverse (Y) directions (TD) of the dielectric film in accordance with IPC-TM 650 2.4.41, and in the thickness direction (Z) of the film in accordance with IPC-TM 650 2.4.24. The analysis temperature was -65°C to 260°C.

[0071] <Dielectric property evaluation> Relative permittivity D k , dielectric loss tangent D f was measured using a balanced disk resonator method in accordance with JPCA-FCL01-2006.

[0072] <Metal foil (copper foil) peel strength measurement> The peel strength of one of the two copper foils provided in the metal-clad laminate was measured in accordance with Japanese Industrial Standard JIS C 6481. The peel test was carried out in a room temperature environment, and the peel angle was 90°.

[0073] <Water absorption rate measurement> The water absorption rate was measured according to Japanese Industrial Standard JIS C 6481.

[0074] <Gurley stiffness measurement> The bending resistance of the metal-clad laminate was measured in accordance with Japanese Industrial Standard JIS L 1096.

[0075] <Solder heat resistance test> A solder heat resistance test was conducted in accordance with JIS C 6481. In the test, pretreatment was performed under normal conditions, and the solder bath temperature was 260°C. Note that normal conditions mean that pretreatment did not involve boiling in hot water. In other words, this means that the metal-clad laminate to be tested was immersed in a solder bath without any moisture.

[0076] The various measurement results are summarized in Table 3 below. In Table 3, the row "Linear thermal expansion coefficient CTE X / Y / Z" shows the CTE in the longitudinal X-axis direction, the CTE in the transverse Y-axis direction, and the CTE in the thickness Z-axis direction, in that order.

[0077] [Table 3]

[0078] As shown in Table 3, Example 1, in which the first fluororesin layer was present between two polyimide layers, satisfied all of the dielectric properties, heat resistance, and dimensional stability at high levels, and also had high bending resistance. Furthermore, in Example 1, the dielectric having a plane-symmetrical laminate structure had two polyimide layers located away from the virtual plane of symmetry, so it exhibited excellent bending resistance in both the MD and TD directions.

[0079] The present invention is not limited to the above-described embodiment, and may be implemented without departing from the gist of the invention. Various modifications are possible within the scope of the present invention. In this case, a combination effect can be obtained. The invention includes various combinations selected from the disclosed constituent elements. For example, some constituent elements can be extracted from all the constituent elements shown in the embodiment. If the problem can be solved and the desired effect can be obtained even if the constituent element is deleted, The composition can be extracted as an invention. The inventions described in the claims of the present application as originally filed are set forth below. [1] A first fluororesin layer containing polytetrafluoroethylene and a powder filler; a polyimide layer provided on each of both surfaces of the first fluororesin layer and containing polyimide; a second fluororesin layer provided on the polyimide layer and containing a perfluoroalkoxyalkane; a metal-clad laminate comprising a metal foil provided on the second fluororesin layer. [2] The metal-clad laminate according to [1], having a total thickness in the range of 50 μm to 200 μm. [3] The metal-clad laminate according to [1] or [2], wherein the total thickness of the polyimide layers is within the range of 10 μm to 50 μm. [4] The metal-clad laminate according to any one of [1] to [3], wherein the volume ratio of the powdery filler in the first fluororesin layer is in the range of 40% to 60%. [5] The metal-clad laminate according to any one of [1] to [4], wherein the metal foil is a copper foil. [6] The continuous use temperature measured by the solder heat resistance test in accordance with JIS C 6481 is 260°C or higher. The metal-clad laminate according to any one of [1] to [5], wherein the metal foil has a peel strength of 1.0 kN / m or more at room temperature. [Explanation of symbols]

[0080] 1...first fluororesin layer, 2...polyimide layer, 3...second fluororesin layer, 4...metal foil, 5...dielectric, 10...metal-clad laminate.

Claims

1. A metal-clad laminate having a total thickness in the range of 50 μm to 200 μm, a first fluororesin layer containing polytetrafluoroethylene and a powder filler; a polyimide layer provided on each of both surfaces of the first fluororesin layer and containing polyimide; a second fluororesin layer provided on at least one of the polyimide layers and containing a perfluoroalkoxyalkane; a metal foil provided on the second fluororesin layer, a PI thickness ratio expressed as ([total thickness of the polyimide layer] / [total thickness of the dielectric])×100 is in the range of 10 to 25%, The total thickness of the dielectric is the thickness of the metal-clad laminate excluding the metal foil.

2. 2. The metal-clad laminate according to claim 1, wherein the total thickness of the polyimide layers is in the range of 10 μm to 50 μm.

3. 3. The metal-clad laminate according to claim 1, wherein the volume ratio of the powdered filler in the first fluororesin layer is in the range of 40% to 60%.

4. The metal-clad laminate according to any one of claims 1 to 3, wherein the metal foil is a copper foil.

5. The continuous use temperature measured by the solder heat resistance test in accordance with JIS C 6481 is 260°C or higher, The metal-clad laminate according to any one of claims 1 to 4, wherein the metal foil has a peel strength of 1.0 kN / m or more at room temperature.

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